Is your Bump map a .jpeg image or is it a .bum image that Poser 4 uses?
I have noticed that sometimes if you use the Poser 4 .bum image as a bump map in Poser 6 or 5 it looks similar to this. If your bump map is a .bum image, try just using the bump .jpeg image instead and see if it still gives you the same result.
I hope what I wrote makes senses... :)